Samsung’s 840 Series SSD reviewed

Samsung's latest is a good drive for the price, but not fantastic.

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Samsung is the biggest producer of flash memory in the world—by a fair margin. The latest numbers from IHS iSuppli peg Samsung's share of the NAND market at over 42 percent, well ahead of Toshiba's at 25 percent and Micron's at 21 percent. Given those figures, it's no surprise Samsung is also one of the biggest players in the SSD business.

What may surprise you is just how long Samsung has been one of the top dogs in that realm. Everyone's familiar with the 830 Series, which debuted a little more than a year ago and quickly became one of the most desired SSDs among PC enthusiasts. The 830 Series was a follow-up to the 470 Series, which didn't make as big of a splash in hobbyist circles. Samsung had other SSDs before that, but I bet you can't name any of them.

I'm sure you can list a few major PC makers, though. Samsung claims it's been the number-one supplier of SSDs to the big-name PC brands since 2006, a full two years before Intel's first SSD even hit the market.

With the PC establishment seemingly sewn up, Samsung has increasingly targeted customers who buy drives one at a time rather than in lots of a thousand. The size of this market is growing as SSDs become more affordable for upgraders and system builders. Right now, the sweet spot is around $200, where there are numerous drives in the 240-256GB range. One of those options is Samsung's next-generation 840 Series SSD.

While the name suggests this drive is a successor to the 830 Series, the new model isn't quite a direct heir. Yes, the controller has been updated and the NAND is built using a smaller fabrication process. However, Samsung has traded the 830 Series' MLC flash for TLC chips that squeeze an extra bit into each cell. This NAND costs less per gigabyte, which is probably why the 840 Series 250GB rings in at just $180 right now. The implications of that extra bit go beyond pricing, affecting not only the drive's performance, but also its longevity. Let's take a closer look.

The skinny on TLC

TLC NAND is the defining characteristic of the Samsung 840 Series. Thankfully, I can assure you it has nothing to do with the television network responsible for spawning Here Comes Honey Boo Boo. TLC stands for "triple-level cell" and describes the number of bits (three) stored in each flash cell. The MLC NAND commonly found in consumer-grade SSDs packs two bits per cell, while the SLC flash reserved for uber-expensive server drives has only one bit.

More bits per cell translate to more gigabytes per die, which in turn means more gigabytes per wafer. MLC doubles the storage capacity of SLC, and TLC adds 50 percent on top of that. By adding bits, the capacity of each wafer can be increased without shrinking the fabrication process.

TLC NAND isn't a new technology; flash makers have been cranking out it for years. The triple-stuffed NAND has mostly been confined to devices like thumb drives because its endurance and performance haven't measured up to MLC NAND. For a sense of why that is, it helps to have an understanding of how data is stored in flash memory. Behold my crudely drawn flash cell diagram:

Each flash cell consists of insulated control and floating gates situated above a silicon substrate. If enough voltage is applied to the control gate, electrons will rise up from the substrate and into the floating gate through a process called tunneling. When the voltage to the control gate is cut, the oxide insulator traps the migratory electrons in the floating gate. The presence of those electrons creates a negative charge that changes the threshold voltage required to activate the cell, effectively writing data to it. Applying a sufficiently strong negative charge to the substrate reverses the process, causing electrons in the floating gate to return to the substrate. This mass exodus erases the cell and returns the threshold voltage to its lowest state.

Because there's some variation in the characteristics of individual cells, any data that's written needs to be read for verification. Data is read by asserting a voltage at the control gate and checking for current flow between the source and the drain. Current will flow if the control voltage is higher than the threshold voltage of the cell.

Reading and writing SLC NAND is fairly quick because there are only two values to consider: 0 and 1. Additional control voltages must be applied to account for the 00, 01, 10, and 11 values supported by MLC NAND, and that takes more time. The process is even longer with TLC flash, which can store eight different values between 000 and 111, requiring more control-voltage levels.

Dealing with TLC flash becomes even more challenging as the NAND starts to wear out. Electrons tunneling through the oxide layer can break down the bonds in the insulator and become trapped. The negative charge created by these stranded electrons raises the minimum threshold voltage required to activate the cell, narrowing the voltage range that can be used for programming. The more values that are crammed within that shrinking voltage range, the more difficult it is to distinguish between them. That's why TLC NAND typically tolerates fewer write-erase cycles than MLC flash, which is itself less durable than SLC NAND. Eventually, the tunneling oxide degrades to the point where the cell is no longer viable and has to be retired.

Transitioning to finer fabrication nodes reduces NAND longevity even further because the layer of tunneling oxide gets thinner as the cell geometry shrinks. That detail is particularly important for the Samsung 840 Series, whose TLC chips are fabbed on a next-gen 21-nm process. The 830 Series uses 27-nm NAND.

Should you be concerned? Maybe. Unlike some SSD makers, Samsung doesn't quote endurance ratings on its website or in the official Reviewer's Guide attached to the 840 Series. We've asked the firm on multiple occasions to characterize the drive's endurance, in terms of either the number of write-erase cycles the NAND can survive or the total volume of writes the drive can withstand as a whole, and we're still waiting for a response.

To its credit, Samsung covers the 840 Series with the same three-year warranty that applies to the 830 Series. The firm also says the NAND rolling off its production lines is sorted, and that only the highest quality chips are used in its SSDs. We've already seen Intel cherry pick high-endurance MLC NAND for enterprise-oriented drives that would have otherwise used SLC memory. Samsung appears to be doing something similar with TLC memory and consumer SSDs. Given how popular MLC-based offerings have become with the server crowd, we're not inclined to write off the 840 Series due solely to its use of TLC NAND.

Why no mention of the 840 Pro? I've read through the first two pages already and see no hint of it?

To be completely honest I didn't read the whole report (as 12 pages of review on a SSD when I have one already is not my cup of tea - not that I'm complaining though, it's great to see such thorough articles) but when I jumped to the last page I did find this:

Quote:

Those expecting the Samsung 840 Series to be a true successor to the 830 Series will no doubt be disappointed. The new drive is slower than its predecessor overall and quite sluggish with both sequential and random writes. Samsung's use of TLC memory is almost certainly to blame for the slower write performance, but the firm hasn't bet the farm on triple-stuffed NAND. The 840 Pro is the true follow-up to the 830 Series, and it features MLC chips with two bits per cell. Of course, the Pro also costs 50% more than the 840 Series. Clearly, it's a different class of drive.

I'm waiting for the 64GB version. For my OS/Drivers/Browser is more than enough. So long I'm using the Intel's X-25V ( 37GB ) and have 12GB free space. For games and media generally, even 128GB is not enough. Greater capacities -still too expensive. The two things I care mostly are, responsiveness and silence. Both will work out well, I guess. Currently the only thing that produces noise is my HDD -WD Black. I'd really like to move entirely on SSDs.

As much as I was trusting Intel in this field, now Samsung got the spot in my heart ( not that I don't trust Intel anymore ).

basically no reason to get the 840 instead of the 830. 830 is going to last longer and be faster in many instances... tricky samsung to do this switch and now make the 840 PRO be what the 830 used to be for more money.

Finally got around to building a new PC last week and went with an 830. Everything I read up until now lists that as one of the best options and I picked up one of the last 256GB models at the Microcenter that just opened up nearby (weeee!) Glad I went with that instead of the 840. I just hadn't read much about the 840's yet and didn't want to take the risk. Looks like a good move.

Awesome Review, currently looking for an SSD and didn't know too much about the technology so this is greatly appreciated. I like Ars for articles like that. Even if it looks like overkill you can get a one-pager everywhere else. But if you really are interested in some specifics you will definitely find them here.

Hey ars, this is a great article and all, but for the sake of reference, would it kill you to have a jump-list for the pages? Reviews like these are quite long and they usually are structured. A mention of that structure would be quite helpful, and links to the pages of each topic would be even better.

I already know the details of TLC and this SSD in particular. I just wanted to read your comments and findings, and having to scan each individual page is annoying just to get to where the info is. I know it's just a small issue, but still. It's the only thing that's ever bothered me of your reviews.

basically no reason to get the 840 instead of the 830. 830 is going to last longer and be faster in many instances... tricky samsung to do this switch and now make the 840 PRO be what the 830 used to be for more money.

TLC is here to stay, and they had to start at some point. I'm glad they did. It should bring prices down pretty fast. Let's remember this is one of the first consumer drives to use TLC, so advantages won't be that obvious right now. People used to say the same thing back in the day when speaking of SLC vs MLC.

12 pages of SSD review seems a bit much, I'll have to dig more into the benchmarking section, but this section runs contrary to what I've read elsewhere:

Quote:

Those expecting the Samsung 840 Series to be a true successor to the 830 Series will no doubt be disappointed. The new drive is slower than its predecessor overall and quite sluggish with both sequential and random writes. Samsung's use of TLC memory is almost certainly to blame for the slower write performance, but the firm hasn't bet the farm on triple-stuffed NAND. The 840 Pro is the true follow-up to the 830 Series, and it features MLC chips with two bits per cell. Of course, the Pro also costs 50% more than the 840 Series. Clearly, it's a different class of drive.

While others at oc's have suggested the 840 has higher random r/w but slower sequential.

Edit: After looking at results between both articles I'm not sure which I believe more, I'll likely continue to go with whichever is cheaper in standard user machines, and the 830's in heavy use environments due to the increased longevity.

The SSD to get (as many readers including you) point out earlier is the Samsung 830 before they go out of stock. IMO the intel 335 drive is fantastic as well. If you can wait, prices on that will come down for thanksgiving sales.

The SSD to get (as many readers including you) point out earlier is the Samsung 830 before they go out of stock. IMO the intel 335 drive is fantastic as well. If you can wait, prices on that will come down for thanksgiving sales.

The 335 is a move to smaller process NAND, which usually results in endurance reductions. Anand also saw a marked reduction in endurance, when testing the Intel 335 (compared the the 330). So again, you are probably better off getting an older Intel 330 drive.

I recently put in an SSD, I chose an Intel 330 drive. It was near tossup with the Samsung 830, but local shops had Intel 330 in stock, I would need to order the Samsung.

Those expecting the Samsung 840 Series to be a true successor to the 830 Series will no doubt be disappointed. The new drive is slower than its predecessor overall and quite sluggish with both sequential and random writes. Samsung's use of TLC memory is almost certainly to blame for the slower write performance, but the firm hasn't bet the farm on triple-stuffed NAND. The 840 Pro is the true follow-up to the 830 Series, and it features MLC chips with two bits per cell. Of course, the Pro also costs 50% more than the 840 Series. Clearly, it's a different class of drive.

I now feel even better for buying that 830

Me too - I literally ordered some 512 gig 830's yesterday and the first reaction I had when I saw the article was 'ohboy.. I could've picked better' .. As I saw the tests,though, I'm starting to really feel comfortable in my choice

While others at oc's have suggested the 840 has higher random r/w but slower sequential.

Edit: After looking at results between both articles I'm not sure which I believe more, I'll likely continue to go with whichever is cheaper in standard user machines, and the 830's in heavy use environments due to the increased longevity.

Anandtech's article is on the 840 Pro, not the regular 840. The 840 Pro absolutely bests the 830.

While others at oc's have suggested the 840 has higher random r/w but slower sequential.

Edit: After looking at results between both articles I'm not sure which I believe more, I'll likely continue to go with whichever is cheaper in standard user machines, and the 830's in heavy use environments due to the increased longevity.

Anandtech's article is on the 840 Pro, not the regular 840. The 840 Pro absolutely bests the 830.

No, it clearly compares the 830, the 840, and the 840 Pro.

Edit: I do see the 830 ahead of the standard 840 on some sequential tests, I was wrong to say 'on all speed tests', which supports the comments I previously heard about the 840 having higher random but slower sequential r/w speeds than the 830.

Edit: I do see the 830 ahead of the standard 840 on some sequential tests, I was wrong to say 'on all speed tests', which supports the comments I previously heard about the 840 having higher random but slower sequential r/w speeds than the 830.

Actually the 840 only loses on sequential write afaict, which is only when you're transferring large files, otherwise the 840 wins pretty much across the board.

I'm more worried about both of anand's 840s dying rather than sequential write being a lot lower than the 830.

These articles are (as mentioned) from the excellent techreport.com. If you know the source, you'd know that you can read their conclusion about the device for a good summary including a value graph. So just read the intro and the conclusion. 2 pages all set.

If anyone from TR/Ars staff is reading, please consider an index for the TR articles. TR itself has a selectbox(boo) which we can use to jump between pages. Ars is not so great in this regards because the articles are generally not this long. Thx.

I have read much more than that before buying my first SSD. I have decided to buy Intel 520 240GB SSD for my laptop.

I value reliability over everything else. If you decide to buy the retail *k5 version, then you get a 5 year warranty without usage restrictions (media wearout indicator E9 warrany limitation). What good is initial cost/GB if those gigabytes of stored data vanish into 0. I'd consider other SSDs, but only if put into a RAID 1 setup. But RAID is basically a no go for laptops.

It’s a very neat solution. You still have access to your optical drive, if you need it. But the main benefit is: - you still have your 1 TB HDD for storage - you can set up an automatic backup service to daily copy your important data to a HDD - you minimize the odds of losing data in the even that something might go wrong with the (cheaper) SSD of your choice

Is the OP tool cross-platform? In other words, can I toss it into my laptop running a Kubuntu/WinXP dual-boot and reconfigure the drive from Kubuntu, since Windows doesn't handle lvm/ex4?

Also, is the OP tool writing to the firmware on the drive or is the drive just detecting unallocated space and using that as OP? While writing to the firmware might be desirable for a number of reasons, the unallocated space would make it so that the user isn't necessarily locked into proprietary software.

One thing that stuck out to me is the disparity between read and write performance. Many readers are fixating on the conclusion paragraph that mentions:

Quote:

The new drive is slower than its predecessor overall and quite sluggish with both sequential and random writes.

I think the distinction deserves to be made here that while you are losing out on performance, this is limited completely to writes. You are not compromising when it comes to read speed - it seems across the board improved and close to best in class. It's at least another thing to consider if you're deciding whether this new product has any merits.

For me, I'm not sure it makes up for the dramatic drop in write speed, though, but how do we quantify? I find myself wondering, over an average 4 hour use-case... How many MB are written vs. read? How much time spent waiting, writing vs. reading? Is there a disparity between the two as far as effect on user experience? (e.g. I imagine I personally spend a lot more time waiting for PCs to boot up, than I do to shutdown)

I think the only other place it excels is power efficiency... unmatched for idle consumption. For all the hours your current laptop is used on battery, how much of that time is the disk sitting completely idle? Also it'd be nice to see just one or two more data points on the power consumption, like one for sequential read and one for sequential write. It's interesting to note that the only load-power data point we have is from one of the very few tests where the 840 shows some improvement (32 concurrent I/Os).

Honestly I'd probably stick to the 830 for desktop use, and consider the 840 for my laptop.

Are you saying greatest stability as in the market, or just SandForce? If the former, that's a joke. If the latter, that's like saying the least offensive mass murderer.

Intel did extensive validation of the SandForce controller and bugfixes for found bugs were rolled only into Intel's proprietary firmware. Most of the current generation of drives are based on SandForce controller.

Are you saying greatest stability as in the market, or just SandForce? If the former, that's a joke. If the latter, that's like saying the least offensive mass murderer.

SSDs with Intel validated Sandforce are among the most reliable consumer SSDs on the market.

The thing to really avoid is new models with new flash, and new firmware (like the one reviewed here). Anandtech reviewed the new 840 Pro, it died during testing. Then Anand received a replacement, and then the replacement also bricked under testing.

I would suggest they're reliable enough to make RAID-1 pointless in all but the most extreme business-critical environments, provided you have backups. I still mirror my spinning disks, but I don't bother with the SSDs at home. SSDs are fairly (though not entirely) immune to that particular problem that HDDs have - spitting out a recoverable error which may mean that your data is safe but what you're working on now is buggered. I think that's the greatest thing that a mirror spares you.

I don't trust the reliability of SSDs all that much. I have a Crucial M4 in the work laptop I'm on now and it died after just five months of use. I'm on the replacement now.

Also, SSDs fail suddenly. With traditional hard drives, you can usually tell when a drive is failing because there might be NTFS errors in the event log, performance might drop off when the hard drive is written to or read from, SMART data will display errors or warnings, or there might be an audible clicking noise. You usually have plenty of time (up to days or weeks) to detect the symptoms and make sure you have your important data backed up.

When my SSD died, my computer just hard locked a couple of times one morning and then BSOD'd after I tried to boot it up the second time. After that, I simply could not get it to boot any more. I was also not able to recover any data from the drive.